Method and system for engine cold start and hot start control

ABSTRACT

Methods and systems are provided for controlling exhaust emissions by adjusting an injection profile for fuel injected into an engine cylinder from a plurality of fuel injectors during engine start and crank. By splitting injection of fuel during start so that a portion of fuel is port injected and a remaining portion is direct injected as one or multiple injections, the soot load of the engine can be reduced and fuel economy can be improved.

FIELD

The present application relates to methods and systems for controllingfuel injection in an engine system.

BACKGROUND AND SUMMARY

Engines may be configured with direct fuel injectors that inject fueldirectly into a combustion cylinder (direct injection), and/or with portfuel injectors that inject fuel into a cylinder port (port fuelinjection). Direct injection allows higher fuel efficiency and higherpower output to be achieved in addition to better enabling the chargecooling effect of the injected fuel.

Direct injected engines, however, also generate more particulate matteremissions (or soot) due to diffuse flame propagation wherein fuel maynot adequately mix with air prior to combustion. Since direct injection,by nature, is a relatively late fuel injection, there may beinsufficient time for mixing of the injected fuel with air in thecylinder. Similarly, the injected fuel may encounter less turbulencewhen flowing through the valves. Consequently, there may be pockets ofrich combustion that may generate soot locally, degrading exhaustemissions.

One approach for reducing particular matter emissions generated bydirect injection of fuel is shown by Bidner et al. in US2011/0162620.Therein, an amount of fuel injected into the cylinder, between thedirect injector and the port fuel injector, is adjusted based on theamount of particulate matter (PM) produced by the engine. For example,as a soot load increases, a fuel injection amount from the directinjector is decreased while a fuel injection amount from the portinjector is correspondingly increased.

However, the inventors herein have identified potential issues with suchan approach. During selected engine operating conditions, even with theshift towards more direct injection, particular matter emissions may notbe sufficiently reduced to meet the mandated low PM emission standards.For example, the direct injection may be performed too late such that bythe time the direct injection occurs, the emitted PMs are higher thanemission standards.

The above issues may be at least partly addressed by a method for anengine comprising: during a first combustion event since engine start,port injecting a portion of fuel during a closed intake valve event; anddirect injecting a remaining portion of the fuel over multipleinjections of the first combustion event. In this way, benefits from aninjection split between a port injection and a direct injection, as wellas benefits from multiple direct injections can be synergized.

In one example, during an engine start, an engine control system mayinject fuel into a cylinder, on the first cylinder combustion event, asa first port injection delivered during a closed intake valve event(e.g., during an exhaust stroke), a second direct injection deliveredduring a compression stroke, and a third direct injection during anintake stroke. This may constitute a first injection profile. The sameinjection profile may be continued during cranking for a number ofcombustion events, based on the cylinder event number (e.g., up tocylinder event number 24). By injecting a portion of the fuel as a portinjection and a remaining portion of the fuel as a direct injection, anexhaust catalyst temperature can be rapidly increased to a light-offtemperature, improving engine performance at engine cold-starts. By alsosplitting the direct injection so that some of the direct injected fuelis injected during the compression stroke and the remaining part of thedirect injected fuel is injected during the intake stroke, the catalystlight-off temperature can be attained without raising exhaustparticulate matter (PM) emissions and degrading engine combustionstability. At the same time fuel economy is improved. After a targetcylinder combustion event number is reached, the injection profile maybe transitioned to a second injection profile that is configured foridle engine speed control. The second injection profile may include, forexample, only port injection of fuel, only direct injection of fuel,and/or a split ratio that is different from the split ratio of the firstinjection profile, with a higher percentage of direct injected fuel. Instill further embodiments, the injection profile during an engine coldstart may vary based on the engine temperature at the cold start (e.g.,based on whether it is a regular temperature engine cold start or a verycold temperature engine cold start).

In this way, by using a split injection profile that splits a fuelinjection between a port injection and multiple direct injections, anactivation time for an exhaust catalyst can be reduced while producinglower gaseous and particulate matter emissions. At the same time, ahigher amount of spark retard can be tolerated without affectingcombustion stability. As such, this allows fuel injection to beoptimized so as to enable the benefits of a fuel injection split betweena port injection and direct injection to be synergized with the benefitsof multiple direct injections. Overall, engine performance is improved,exhaust emissions are improved, and further, fuel economy is alsoimproved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example combustion chamber.

FIG. 2 shows a high level flow chart for adjusting fuel injection duringengine start and crank operations to reduce an engine soot load.

FIGS. 3-4 show example fuel injection profiles used during differentengine start and crank operations, according to the present disclosure.

DETAILED DESCRIPTION

The following description relates to systems and methods for adjustingan engine fuel injection, such as in the engine system of FIG. 1, duringengine start and crank to reduce a soot load of the engine. An enginecontroller may perform a control routine, such as the routine of FIG. 2,to adjust a fuel injection profile, including an amount of fuel portinjected to a cylinder and an amount of fuel direct injected overmultiple injections into the cylinder, during an engine start and duringcranking. The profile may be adjusted based on each of an exhaustcatalyst temperature and a cylinder event number so as to expeditecatalyst activation while reducing exhaust PM emissions and withoutdegrading combustion stability. By using a fuel injection profile from aprofile having a relatively higher amount of port injection duringengine start and crank, and then transitioning to a fuel injectionprofile having a relatively higher amount of compression stroke directinjection, an engine cold-start performance can be increased whilelowering an engine soot load and without degrading engine fuel economy.Example adjustments are shown at FIGS. 3-4.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (i.e.combustion chamber) 14 of engine 10 may include combustion chamber walls136 with piston 138 positioned therein. Piston 138 may be coupled tocrankshaft 140 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 140 may be coupledto at least one drive wheel of the passenger vehicle via a transmissionsystem. Further, a starter motor may be coupled to crankshaft 140 via aflywheel to enable a starting operation of engine 10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 162 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 162 may be disposed downstreamof compressor 174 as shown in FIG. 1, or may alternatively be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be any suitable sensor for providing an indication ofexhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO(universal or wide-range exhaust gas oxygen), a two-state oxygen sensoror EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor.Emission control device 178 may be a three way catalyst (TWC), NOx trap,various other emission control devices, or combinations thereof.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 via actuator 152.Similarly, exhaust valve 156 may be controlled by controller 12 viaactuator 154. During some conditions, controller 12 may vary the signalsprovided to actuators 152 and 154 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve150 and exhaust valve 156 may be determined by respective valve positionsensors (not shown). The valve actuators may be of the electric valveactuation type or cam actuation type, or a combination thereof. Theintake and exhaust valve timing may be controlled concurrently or any ofa possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. Each cam actuation system may include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.For example, cylinder 14 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT. In other embodiments, theintake and exhaust valves may be controlled by a common valve actuatoror actuation system, or a variable valve timing actuator or actuationsystem.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen for example when higher octane fuels or fuelswith higher latent enthalpy of vaporization are used. The compressionratio may also be increased if direct injection is used due to itseffect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including two fuel injectors 166 and 170.Fuel injector 166 is shown coupled directly to cylinder 14 for injectingfuel directly therein in proportion to the pulse width of signal FPW-1received from controller 12 via electronic driver 168. In this manner,fuel injector 166 provides what is known as direct injection (hereafterreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from high pressure fuel system 172 including a fueltank, fuel pumps, a fuel rail, and driver 168. Alternatively, fuel maybe delivered by a single stage fuel pump at lower pressure, in whichcase the timing of the direct fuel injection may be more limited duringthe compression stroke than if a high pressure fuel system is used.Further, while not shown, the fuel tank may have a pressure transducerproviding a signal to controller 12.

Fuel injector 170 is shown arranged in intake passage 146, rather thanin cylinder 14, in a configuration that provides what is known as portinjection of fuel (hereafter referred to as “PFI”) into the intake portupstream of cylinder 14. Fuel injector 170 may inject fuel in proportionto the pulse width of signal FPW-2 received from controller 12 viaelectronic driver 171. Fuel may be delivered to fuel injector 170 byfuel system 172.

Fuel may be delivered by both injectors to the cylinder during a singlecycle of the cylinder. For example, each injector may deliver a portionof a total fuel injection that is combusted in cylinder 14. Further, thedistribution and/or relative amount of fuel delivered from each injectormay vary with operating conditions, such as engine load and/or knock,such as described herein below. The relative distribution of the totalinjected fuel among injectors 166 and 170 may be referred to as a firstinjection ratio. For example, injecting a larger amount of the fuel fora combustion event via (port) injector 170 may be an example of a higherfirst ratio of port to direct injection, while injecting a larger amountof the fuel for a combustion event via (direct) injector 166 may be alower first ratio of port to direct injection. Note that these aremerely examples of different injection ratios, and various otherinjection ratios may be used. Additionally, it should be appreciatedthat port injected fuel may be delivered during an open intake valveevent, closed intake valve event (e.g., substantially before an intakestroke, such as during an exhaust stroke), as well as during both openand closed intake valve operation.

Similarly, directly injected fuel may be delivered during an intakestroke, as well as partly during a previous exhaust stroke, during theintake stroke, and partly during the compression stroke, for example.Further, the direct injected fuel may be delivered as a single injectionor multiple injections. These may include multiple injections during thecompression stroke, multiple injections during the intake stroke, or acombination of some direct injections during the compression stroke andsome during the intake stroke. When multiple direct injections areperformed, the relative distribution of the total directed injected fuelbetween an intake stroke (direct) injection and a compression stroke(direct) injection may be referred to as a second injection ratio. Forexample, injecting a larger amount of the direct injected fuel for acombustion event during an intake stroke may be an example of a highersecond ratio of intake stroke direct injection, while injecting a largeramount of the fuel for a combustion event during a compression strokemay be an example of a lower second ratio of intake stroke directinjection. Note that these are merely examples of different injectionratios, and various other injection ratios may be used.

As such, even for a single combustion event, injected fuel may beinjected at different timings from a port and direct injector.Furthermore, for a single combustion event, multiple injections of thedelivered fuel may be performed per cycle. The multiple injections maybe performed during the compression stroke, intake stroke, or anyappropriate combination thereof.

As elaborated with reference to FIGS. 2-4, a controller may adjust afuel injection profile during a first cylinder combustion event atengine start (in particular, an engine cold start), so as to takesynergistic advantage of both a port injection and multiple directinjections to expedite exhaust catalyst activation without increasing anengine soot load and while also providing fuel economy benefits. Thefirst injection profile used at the engine start may have apredetermined first and second injection ratio that enables catalysttemperature control. The first injection profile may be continued intoengine crank until a target cylinder event number since the firstcombustion is reached. Then, fuel injection may be transitioned to asecond, different injection profile, having a different first and secondinjection ratio that enables idle engine speed control.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel injectors 166 and 170 may have different characteristics. Theseinclude differences in size, for example, one injector may have a largerinjection hole than the other. Other differences include, but are notlimited to, different spray angles, different operating temperatures,different targeting, different injection timing, different spraycharacteristics, different locations etc. Moreover, depending on thedistribution ratio of injected fuel among injectors 170 and 166,different effects may be achieved.

Fuel tank in fuel system 172 may hold fuel with different fuelqualities, such as different fuel compositions. These differences mayinclude different alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.In one example, fuels with different alcohol contents could includegasoline, ethanol, methanol, or alcohol blends such as E85 (which isapproximately 85% ethanol and 15% gasoline) or M85 (which isapproximately 85% methanol and 15% gasoline). Other alcohol containingfuels could be a mixture of alcohol and water, a mixture of alcohol,water and gasoline etc.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed. An example routine that maybe performed by the controller is described at FIG. 2.

Now turning to FIG. 2, an example routine 200 is shown for controlling afuel injection to an engine cylinder including a (first) port injectorand a (second) direct injector based on an amount of particulate matterproduced by the engine.

At 202, engine operating conditions may be estimated and/or measured.These may include, for example, engine speed, engine load, cylinderair-to-injected fuel ratio (AFR), engine temperature (for example, asinferred from an engine coolant temperature), exhaust temperature,catalyst temperature (Tcat), desired torque, boost, etc.

At 204, it may be determined whether an engine cold-start condition ispresent. As such, an engine cold-start may include an initial enginestart from shutdown conditions. In one example, an engine cold-startcondition may be confirmed if an engine temperature is below a thresholdand a catalyst temperature is below a threshold (such as below alight-off temperature). If an engine cold-start condition is notconfirmed, at 206, an engine hot-start condition may be confirmed. Assuch, the engine hot-start may include an engine restart wherein theengine is restarted soon after a preceding engine shut-down. In oneexample, an engine hot-start condition may be confirmed if an enginetemperature and/or a catalyst temperature is above a threshold.

In response to an engine cold-start condition, at 210, the routineincludes operating the engine with a first injection profile to expeditecatalyst activation. Operating with the first injection profileincludes, during a first combustion event since engine start, portinjecting a portion of fuel during a closed intake valve event, anddirect injecting a remaining portion of the fuel over multipleinjection. Injecting the remaining portion of fuel over multipleinjections may include direct injecting the remaining portion as atleast an intake stroke injection and a compression stroke injection. Forexample, as elaborated with reference to FIG. 3, the direct injectedportion of the fuel may be delivered as a first intake stroke injectionand a second compression stroke injection. The injection amounts may beadjusted such that the port injection amount, the first intake strokeinjection amount, and the second compression stroke injection amount arewithin 15% of each other. In one example, 30% of the fuel injection maybe delivered as a port injection during a closed intake valve event(e.g., during an exhaust stroke), another 35% of the fuel injection maybe delivered as an intake stroke direct injection, while a remaining 35%of the fuel injection is delivered as a compression stroke directinjection.

A first ratio of the port injection amount relative to a total directinjection amount may be adjusted based on an exhaust catalysttemperature. For example, as the catalyst temperature increases, ahigher ratio of port injection may be used. The first ratio may befurther based on the cylinder combustion event number at engine start. Asecond ratio of the first intake stroke injection amount relative to thesecond compression stroke injection amount may be adjusted based on theexhaust catalyst temperature and soot tendencies of the engine. Thesecond ratio may be further based on the cylinder combustion eventnumber at engine start. Herein, the relatively higher amount of directinjection may be advantageously used to heat the engine and catalyst,thereby expediting catalyst activation and improving engine and catalystperformance under engine cold-start conditions.

In addition to the first injection profile, spark timing may be retardedbased on the exhaust catalyst temperature at the engine start. Forexample, to supply additional heat to the exhaust catalyst, the sparktiming may be retarded further from MBT. The amount of spark retardapplied may be further based on each of the first and second ratios. Forexample, as the first or second ratio increases, spark timing may beadvanced or retarded for combustion stability. For most engines that areoperating at extremely retarded spark, the second ratio is increased toa level for best combustion at least PM emission.

At 212, the routine includes continuing the port injecting and directinjecting over multiple fuel injections during cranking. In particular,the continuing is performed for a number of combustion events since thefirst combustion event, the number based on a cylinder event number. Assuch, the starting of an engine is a large transient event and havingthe ability to manage each event enables more robust engine performanceand lower gaseous and particulate emissions. Further, since enginecombustion chambers vary in capabilities, the routine's ability tomanage each event enables a strategy that is flexible enough to workwith different types of engines.

During engine start, the first event is fueled when the engine speed isaround 150 to 200 rpm. Each event after that is fueled at a differentengine speed. For low emission engines and power-trains, it is importantto have flexibility in the fueling during engine start as the optimumemission/performance injection type and timing may be different for eachevent. For example, extreme cold starts can be a challenge for both Portand Direct Injection systems for different reasons. Port injectionsystems lose a lot of fuel into the crankcase. This dilutes the oilwhile the engine has trouble getting enough fuel to vaporize in cylinderto start. At extreme cold temperatures, the higher fuel pressure ofdirect injection works well to produce enough vaporized fuel to combust,but the displacement type high pressure fuel pump systems struggle tomaintain fuel pressure at the high fuel demand of the cold start at lowcranking speeds. Thus, at extreme cold starts, the first combustioncycle may have the port injection system supplementing the fuel so thatthe direct injection system can deliver appropriately sized compressioninjections for robust start at extreme cold temperatures. After a cycle,the engine speed may be sufficient for the direct injection high fuelpump to maintain the desired pressure for fuel vaporization andefficient combustion. At that point, the port injection of fuel can besuspended until the engine warms up.

As another example, a different fuel injection adjustment may beperformed at the restart of an engine at operating temperature (or hotstart). Here, for the quickest start, direct injection of fuel may beused for the first revolution. Then, port injection of fuel may beadded. The result is a faster engine start with lower PM emissions. Asyet another example, at extreme hot start temperatures, the fuel in thelow pressure port injection fuel rail may become vapor while the directinjection high pressure keeps the fuel liquid. Thus, at extreme hotoperating temperatures, the first cycle may have a low first ratio suchthat mainly direct injection is used to start the engine. Then, thefirst ratio may be increased, removing vapor from the port injectionsystem and cooling the port fuel rail as cooler fuel comes into it.

At 218, it may be determined if the engine speed is higher than athreshold speed. In particular, it may be determined if cranking hasbeen completed and an engine idling speed has been attained. If yes,then at 220, after cranking has been completed, the routine includestransitioning fuel injection to a second injection profile that enablesidle speed control. This may include, for example, transitioning to oneof only port injecting fuel or only direct injecting fuel. In oneexample, the injection profile may be transitioned to a port injectiononly injection profile for engine starts when the engine is above a(first) temperature threshold and below another (e.g., below a secondthreshold higher than the first threshold). In another example, theinjection profile may be transitioned to a direct injection onlyinjection profile for engine start below the (first) temperaturethreshold and above another threshold (e.g., a third threshold lowerthan the first threshold). In an alternate example, the transitioningincludes, after cranking, transitioning fuel injection to port injectinga portion of fuel before the intake valve opens and direct injecting aremaining portion of the fuel during an intake stroke. Herein, theinjection ratio of fuel direct injected to fuel port injected may varybased on fuel mass. As such, at 218, if the threshold engine speed hasnot been attained, then at 219, the injection profile being used atcrank may be maintained.

It will be appreciated that while the routine of FIG. 2 shows a firstinjection profile being used for all engine cold starts, in alternateembodiments, the first injection profile may vary during engine coldstarts based on the engine temperature at the time of the cold start. Inparticular, the first and second injection ratios of the first injectionprofile may vary based on the engine temperature at the time of the coldstart (e.g., based on whether the cold start was a regular cold start ora very cold temperature cold start). For example, at regular enginecold-starts, the first injection profile may have a first and secondinjection ratio that is biased relatively equal while at very coldtemperature cold starts, the first injection profile may have a firstand second injection ratio that is biased relatively more towards directinjection.

Returning to 206, in response to an engine hot-start condition, at 214,the routine includes operating the engine with a second injectionprofile to improve robustness at extreme hot starts. Operating with thesecond injection profile includes, during a first combustion event sinceengine start, port injecting a (larger) portion of fuel during a closedintake valve event, and direct injecting a (smaller) remaining portionof the fuel over multiple injections. Injecting the remaining portion offuel over multiple injections may include direct injecting the remainingportion as at least an intake stroke injection and/or a compressionstroke injection. For example, as elaborated with reference to FIG. 3,the direct injected portion of the fuel may be delivered as a firstintake stroke injection and a second compression stroke injection. Theinjection amounts may be adjusted such that the port injection amount,the first intake stroke injection amount, and the second compressionstroke injection amount are within 15% of each other. In one example,35% of the fuel injection may be delivered as a port injection during aclosed intake valve event (e.g., during an exhaust stroke), another 35%of the fuel injection may be delivered as an intake stroke directinjection, while a remaining 30% of the fuel injection is delivered as acompression stroke direct injection. In another example, 50% of the fuelinjection may be delivered as a port injection during a closed intakevalve event, another 50% of the fuel injection may be delivered as anintake stroke direct injection, and with no fuel injection delivered fora compression stroke direct injection. In yet another example, 70% ofthe fuel injection may be delivered as a port injection during a closedintake valve event with no fuel injection delivered as an intake strokedirect injection, with the remaining 30% of the fuel injection deliveredas a compression stroke direct injection. In a still further example,none of the fuel may be delivered as a port injection during a closedintake valve event, while 70% of the fuel injection is delivered as anintake stroke direct injection, and while a remaining 30% of the fuelinjection is delivered as a compression stroke direct injection. In yeta further example, the port injection amount, the intake stroke directinjection amount, and the compression stroke direct injection amountsmay be 0-100% of each other.

A first ratio of the port injection amount relative to a total directinjection amount may be adjusted based on engine coolant, or cylinderhead measured or inferred temperature during the hot start. For example,as temperatures increase, a higher ratio of port injection may be used.The first ratio may be further based on the cylinder combustion eventnumber. A second ratio of the first intake stroke injection amountrelative to the second compression stroke injection amount may beadjusted based on engine coolant, or cylinder head measured or inferredtemperature and a soot load of the engine. The second ratio may befurther based on the cylinder combustion event number. Herein, therelatively higher amount of direct injection may be advantageously usedto rapidly start the engine, thereby improving engine performance andfuel economy under engine hot-start conditions.

In comparison, if the engine and/or catalyst temperature has increasedand is within a threshold region of the threshold temperature, then at212, the controller may start transitioning the fuel injection to theengine cylinder from the relatively higher amount of port fuel injectionto a relatively higher amount of direct fuel injection. The transitionmay be adjusted based on a distance of the engine and/or catalysttemperature from the threshold temperature. For example, once thetemperature is within a threshold region of the threshold temperature, arate of the transition may be increased as the distance from thethreshold temperature increases. This may include, graduallydeactivating the port injector, while gradually activating the directinjector, as the temperature approaches the threshold temperature. Thus,by the time the engine and/or catalyst temperature is at, or beyond, thethreshold temperature, the fuel injection may have been transitioned toa higher amount of direct fuel injection and a smaller amount of portfuel injection. Herein, by using a higher ratio of direct injection asan engine load (and thus, engine temperature) increases, the chargecooling and improved fuel economy benefits of a direct injected fuel maybe availed.

As an example, if the engine and/or catalyst temperature is above orwithin a threshold region of the threshold temperature, the controllermay determine an engine hot start and correspondingly starttransitioning the fuel injection to the engine cylinder from therelatively higher amount of port fuel injection to a relatively higheramount of direct fuel injection. The transition may be adjusted based ona distance of the engine and/or catalyst temperature from the thresholdtemperature. For example, once the temperature is within a thresholdregion of the threshold temperature, a rate of the transition may beincreased as the distance from the threshold temperature increases. Thismay include, gradually deactivating the port injector, while graduallyactivating the direct injector, as the temperature approaches thethreshold temperature. Thus, by the time the engine and/or catalysttemperature is at, or beyond, the threshold temperature, the fuelinjection may have been transitioned to a higher amount of direct fuelinjection and a smaller amount of port fuel injection. Herein, by usinga higher ratio of direct injection as an engine temperature increases,the charge cooling and improved fuel economy benefits of a direct fuelinjection fuel are achieved.

While the routine of FIG. 2 does not show performing any spark timingadjustments while operating the second injection profile, in alternateembodiments, in addition to the second injection profile, spark timingmay be adjusted (e.g., retarded) based on engine speed and event at theengine hot start. For example, if engine speed increases rapidly perevent, spark timing may be retarded further from MBT. The amount ofspark retard applied may be further based on each of the first andsecond ratios. For example, as the first or second ratio increases,spark timing may be advanced with the first ratio and retarded dependingon the second ratio.

In one example, spark timing adjustments may be selectively performedbased on the fuel injection profile to compensate for torque transients.For example, in response to a decrease in amount of port fuel injectionand increase in the amount of direct fuel injection, spark ignitiontiming may be retarded by an amount. In alternate embodiments,additionally or optionally, adjustments may be made to one or more ofboost, EGR, VCT, etc. to compensate for torque transients.

At 216, the routine includes continuing the port injecting and directinjecting over multiple fuel injections during cranking. In particular,the continuing is performed for a number of combustion events since thefirst combustion event, the number based on a cylinder event number. Aspreviously elaborated, during engine start, the first event is fueledwhen the engine speed is around 150 to 200 rpm, each event after thatbeing fuel with a different engine speed. At extreme cold starts, thefirst combustion cycle may use port injection to supplement the fuel sothat the direct injection system can deliver appropriately sizedcompression injections for robust start at extreme cold temperatures.After a cycle, the engine speed may be sufficient for the directinjection high fuel pump to maintain the desired pressure for fuelvaporization and efficient combustion. At that point, the port injectionof fuel can be suspended until the engine warms up.

In one example, during the engine crank, the fuel injection profile maybe adjusted based on the engine operating conditions as well as the fuelavailable in the fuel tank. In one example, as an engine speed, engineload, and/or desired torque increases during the crank, an amount offuel injected through the direct injector may be increased while anamount of fuel injected through the port injector may be decreased.Herein, the direct injection of the fuel may provide higher fuelefficiency and higher power output. Additionally, when the fuelavailable for injection is an alcohol fuel, the direct injection of thefuel may be used to take advantage of the charge cooling properties ofthe alcohol fuel.

At 218, after cranking, the routine includes determining if the enginespeed is higher than a threshold speed (such as above an engine idlingspeed). If so, the routine includes, at 220, transitioning fuelinjection to a second injection profile that enables idle speed control,as elaborated previously. Else, at 219, the first injection profilebeing used at cranking may be maintained and continued until, an engineidle speed is reached.

In one example, during a first combustion event since engine start, acontroller may port inject a portion of fuel during a closed intakevalve event, and direct inject a remaining portion of the fuel overmultiple injections of the first combustion event. Therein, as oneexample, the remaining portion may be injected as at least a firstintake stroke injection and a second compression stroke injection. Theport injection amount, the first intake stroke injection amount, and thesecond compression stroke injection amount may be adjusted to be within0% to 100% of each other. In an alternate example, the remaining portionof fuel may be injected as multiple intake stroke injections, multiplecompression stroke injections, or at least one intake stroke injectionand at least one compression stroke injection.

A first ratio of the port injection amount relative to a total directinjection amount (that is, a sum of fuel direct injected over one ormore intake strokes, a sum of fuel direct injected over one or morecompression strokes, or a sum of fuel injected as at least an intakestroke injection and at least a compression stroke injection) may beadjusted based on one or more of an exhaust catalyst temperature and anengine temperature. A second ratio of the first intake stroke injectionamount relative to the second compression stroke injection amount maythen be adjusted based on the exhaust catalyst temperature, the enginetemperature and a soot load of the engine. Each of the first and secondratios may be further based on a combustion event number since enginestart.

The controller may also retard spark timing based on the exhaustcatalyst temperature and engine temperature at the engine start.Therein, an amount of spark retard may be further based on each of thefirst and second ratios. The controller may then continue the portinjecting and direct injecting over multiple fuel injections duringcranking following the first combustion event. The continuing may beperformed for a number of combustion events since the first combustionevent during the cranking, wherein the number of combustion events forwhich the continuing is performed is based on a cylinder event number.After cranking, fuel injection may be transition to a third ratio ofport injection to direct injection, and a fourth ratio of intake strokeinjection to compression stoke injection. Herein, the third ratio may bedifferent from the first ratio (e.g., larger or smaller), while thefourth ratio is different from the second ratio (e.g., larger orsmaller). Alternatively, after cranking, fuel injection may betransitioned to port injecting a portion of fuel during a closed intakevalve event and direct injecting a remaining portion of the fuel duringthe intake stroke or compression stroke.

FIG. 3 shows a map 300 of valve timing and piston position, with respectto an engine position, for a given engine cylinder. During an enginestart, while the engine is being cranked, an engine controller may beconfigured to adjust a fuel injection profile of fuel delivered to thecylinder. In particular, fuel may be delivered as a first profile duringthe engine start, and then transitioned to a second, different profilefollowing engine cranking. The differing fuel injection profiles mayinclude a portion of the fuel delivered to the cylinder as portinjection and a remaining portion of the fuel delivered to the cylinderas direct injection. Further, the direct injected portion of fuel may bedelivered as a single intake stroke injection, a single compressionstroke injection, or a combination thereof.

Map 300 illustrates an engine position along the x-axis in crank angledegrees (CAD). Curve 308 depicts piston positions (along the y-axis),with reference to their location from top dead center (TDC) and/orbottom dead center (BDC), and further with reference to their locationwithin the four strokes (intake, compression, power and exhaust) of anengine cycle. As indicated by sinusoidal curve 308, a piston graduallymoves downward from TDC, bottoming out at BDC by the end of the powerstroke. The piston then returns to the top, at TDC, by the end of theexhaust stroke. The piston then again moves back down, towards BDC,during the intake stroke, returning to its original top position at TDCby the end of the compression stroke.

Curves 302 and 304 depict valve timings for an exhaust valve (dashedcurve 302) and an intake valve (solid curve 304) during a normal engineoperation. As illustrated, an exhaust valve may be opened just as thepiston bottoms out at the end of the power stroke. The exhaust valve maythen close as the piston completes the exhaust stroke, remaining open atleast until a subsequent intake stroke has commenced. In the same way,an intake valve may be opened at or before the start of an intakestroke, and may remain open at least until a subsequent compressionstroke has commenced.

As a result of the timing differences between exhaust valve closing andintake valve opening, for a short duration, before the end of theexhaust stroke and after the commencement of the intake stroke, bothintake and exhaust valves may be open. This period, during which bothvalves may be open, is referred to as a positive intake to exhaust valveoverlap 306 (or simply, positive valve overlap), represented by ahatched region at the intersection of curves 302 and 304. In oneexample, the positive intake to exhaust valve overlap 306 may be adefault cam position of the engine present during an engine cold start.

The third plot (from the top) of map 300 depicts an example fuelinjection profile that may used at an engine start, during enginecranking, to reduce an amount of engine start exhaust PM emissionswithout degrading engine combustion stability. As elaborated herein, theinjection profile is adjusted based on combustion event number since anengine start with a portion of fuel port injected (hatched block) and aportion of fuel direct injected (diagonally striped blocks).

In the depicted example, a fuel injection profile used during a firstcombustion event since engine start is depicted. Herein, the enginestart is an engine cold start. An engine controller is configured toprovide the total amount of fuel to the cylinder as a first portinjection depicted at 312 (hatched block), a second direct injectiondepicted at 314 (diagonally striped block), and a third direct injectiondepicted at 316 (diagonally striped block). The first port injection 312may include a first portion of fuel (P1) that is port injected at afirst timing CAD1. In particular, the first portion of fuel is portinjected during a closed intake valve event (that is, during the exhauststroke). Then, a remaining portion of the fuel is direct injected overmultiple injections. In particular, a second portion of fuel (D2) isdirect injected as a first intake stroke injection at CAD2 while a thirdportion of fuel (D3) is direct injected as a second compression strokeinjection at CAD3.

In addition to splitting the amount of fuel injected as a single portinjection and multiple direct injections, a spark ignition timing may beadjusted. For example, spark timing may be advanced towards MBT duringport only injection (as shown at 320), such as when the engine isstarted at extreme cold temperatures. As an alternate example, spark maybe retarded with the addition of a direct compression injection (asshown at 318).

In the depicted example, the fuel injection profile includes a ratio offuel port injected:fuel that is intake stroke direct injected:fuel thatis compression stroke direct injected that is set to 30:35:35. Herein,by port injecting a portion of the fuel and direct injecting a remainingportion of the fuel, an exhaust catalyst temperature can be rapidlyincreased to a light-off temperature, improving engine performance atthe engine cold-start. Further, by splitting the direct injection intoat least a first intake stroke injection and at least a secondcompression stroke injection, the catalyst light-off temperature can beattained without raising exhaust particulate matter (PM) emissions anddegrading engine combustion stability. This allows an engine startemissions to be improved while also improving fuel economy.

Now turning to FIG. 4, map 400 shows example fuel injection profiles401-404 that may be used during an engine start, during cranking, andduring engine idle control. As elaborated herein, the injection profilesmay be adjusted based on a combustion event number since the enginestart, as well as based on whether the engine start is a cold enginestart or a hot engine start. As such, each injection profile depicts atiming of injection relative to a cylinder piston position. Based on theposition of the cylinder's piston at any time in the engine cycle, fuelmay be injected into the cylinder during an intake stroke (I), acompression stroke (C), a power stroke (P), or an exhaust stroke (E).The injection profile further depicts whether fuel was injected via portinjection (hatched blocks), single or multiple direct injections(striped blocks), or both. Further, the injection profile depictswhether any spark timing adjustments were concurrently performed (e.g.,use of spark retard).

A first example injection profile that may be used during an engine coldstart is shown at 401. In particular, first injection profile 401depicts fuel injection to a cylinder during a first cylinder combustionevent (event1). During the engine cold start, a portion of fuel isinjected into the cylinder as a first port injection (hatched block)during a closed intake valve event (that is, during an exhaust stroke ofa previous cylinder combustion event) while a remaining portion of thefuel is injected as a first intake stroke direct injection and a secondcompression stroke direct injection (diagonally striped block). Theinjection amounts may be adjusted such that the port injection amount,the first intake stroke injection amount, and the second compressionstroke injection amount are within 15% of each other. In one example,35% of the fuel injection may be delivered as a port injection during aclosed intake valve event (e.g., during an exhaust stroke), another 35%of the fuel injection may be delivered as an intake stroke directinjection, while a remaining 30% of the fuel injection is delivered as acompression stroke direct injection.

In addition to splitting the amount of fuel injected as a single portinjection and multiple direct injections, a spark ignition timing may beadjusted. For example, at 401, spark timing (solid bar) may be 12degrees before TDC during the port injection.

A second example injection profile that may be used during an engine hotstart is shown at 402. In particular, second injection profile 402depicts fuel injection to a cylinder during a first cylinder combustionevent (event1′) at hot start. The hot start may include an enginerestart from idle stop for example. Alternatively, the hot start mayinclude an engine restart from shut down where the engine has not beenshut down for sufficiently a long duration (and has therefore not cooleddown to ambient temperatures). During the engine hot start, no fuel isinjected into the cylinder as a first port injection while all of thefuel is injected as a direct compression injection (striped block). Theinjection amounts may be adjusted such that the port injection amount,the first intake stroke injection amount, and the second compressionstroke injection amount can be 0% to 100%. In comparison, 40% of thefuel injection may be delivered as a port injection during a start atnormal ambient temperature, another 35% of the fuel injection may bedelivered as an intake stroke direct injection, while a remaining 25% ofthe fuel injection is delivered as a compression stroke directinjection.

In addition to the single port injection during the engine hot start,spark ignition timing may be adjusted. For example, at 402, spark timing(solid bar) may be set at TDC compared to 12 degree before TDC fornormal ambient temperatures.

A third example injection profile that may be used during enginecranking, and after an engine start (hot start or cold start), is shownat 403. In particular, third injection profile 403 depicts fuelinjection to a cylinder for n number of cylinder combustion events sincethe first cylinder combustion event (events 2 through n). During theengine cranking, fuel injection is transitioned to a profile where alarger portion of fuel is port injected into the cylinder during a hotrestart while a smaller remaining portion of the fuel is direct injectedas intake/compression stroke injection. The injection amounts may beadjusted such that the port injection amount and the direct injectionamount are 0% to 100% of each other. In one example, 70% of the fuelinjection may be delivered as a port injection during the cranking whileanother 30% of the fuel injection may be delivered as a compressionstroke direct injection.

In addition to splitting the amount of fuel injected as a single portinjection and a single direct injection, spark ignition timing may beadjusted. For example, at 403, spark timing (solid bar) may be adjustedto 8 degrees before TDC.

A fourth example injection profile that may be used following enginestart and cranking, and after an engine idle speed has been attained isshown at 404. In particular, fourth injection profile 404 depicts fuelinjection to a cylinder for a number of cylinder combustion events sincethe completion of cranking (events n through m). During the engine idlecontrol while the engine is warming up, fuel injection is transitionedto a profile where the portion of fuel port injected into the cylinderis similar to the remaining portion of fuel that is direct injected asan intake stroke injection. Further, no fuel is direct injected duringthe compression stroke. The injection amounts may be adjusted such thatthe port injection amount and the direct injection amount are within 0%to 100% of each other. In addition to splitting the amount of fuelinjected as a single port injection and a single direct injection, sparkignition timing may be adjusted. For example, at 404, spark timing(solid bar) may be retarded 40 degrees from MBT during the portinjection.

In one example, during an engine start and while cranking, based on acylinder event number, fuel may be injected as a first port injectionduring a closed intake valve event, at least one direct injection duringan intake stroke and at least one direct injection during a compressionstroke. The amount of fuel injected in the first port injection, thesecond direct injection, and the third direct injection may be 0% to100% of each other. The injecting may be continued during the enginestart and cranking until a threshold cylinder event number is reached.Then, after the threshold cylinder event number, fuel injection may betransitioned to another closed intake valve port injection and at leastone intake and compression stroke injection. Herein, a first ratio ofport injection to direct injection after the threshold cylinder eventnumber is reached may be different (e.g., larger or smaller) from thefirst ratio of port injection to direct injection before the thresholdcylinder event number is reached. Likewise, a second ratio of intakestroke direct injection to compression stroke direct injection after thethreshold cylinder event number is reached may be different (e.g.,larger or smaller) from the second ratio before the threshold cylinderevent number is reached.

After the threshold cylinder event number is reached, the first ratio ofthe port injection during the closed intake valve event to the directinjection during either the compression stroke or the intake stroke maybe adjusted based on an exhaust catalyst temperature and enginetemperature, with the first ratio of port injection to direct injectionincreased as the exhaust catalyst temperature increases. That is, afterthe threshold cylinder event number, as the exhaust catalyst temperatureincreases, a proportion of port injection in the injection profile maybe increased.

In comparison, before the threshold cylinder event number is reached,the first ratio of the port injection during the closed intake valveevent relative to the direct injection may be adjusted based on anestimated engine soot load, while the second ratio of the intake strokeinjection relative to the compression stroke injection is based on theestimated engine soot load and the first ratio. In some embodiments,such as where the emission control device includes a particulate filter,the ratio may also be adjusted based on whether the engine is in afilter regeneration mode of non-regeneration mode. For example, duringfilter regeneration, the first and second ratios may be adjusted tofavor the port injection of fuel. Then, as the engine runs at stabilizedtemperatures, the first and second ratios may be adjusted to favor firstand second ratios that provide volumetric efficiency benefits and enableknock mitigation.

In an alternate example, an engine system may comprise an engine, afirst port injector coupled to an engine cylinder, a second directinjector coupled to the engine cylinder, and a control system withcomputer readable instructions for operating the engine with differentfuel injection profiles. For example, during a first cylinder combustionevent, and based on a cylinder combustion event number since the firstevent, cylinder fuel injection may be transitioned from a firstinjection profile including a first port injection during a closedintake valve and a second direct injection including at least one intakestroke injection, to a second injection profile including at least onecompression stroke direct injection. Herein, the first injection profileand second injection profile may be based on catalyst temperature,engine temperature and soot load, with a proportion of fuel directinjected in the compression stroke relative to the intake stroke beinghigher in the first injection profile as compared to the secondinjection profile.

In this way, by adjusting an engine fuel injection amount between adirect injector and a port injector based on the cylinder combustionevent number and the catalyst temperature, the fuel efficiency and poweroutput advantages of direct injection may be achieved in addition to thefaster catalyst heating advantages of port injection, all withoutdegrading exhaust emissions. The combination of simultaneous using portand direct injection fuel systems adds robustness to engine startperformance at both extreme cold and hot conditions. In addition, atnominal ambient temperatures, the combination of simultaneous use ofport and direct injection fuel systems enables emissions to beoptimized, especially particulate emissions. As such, the use ofturbocharging and direct injection for fuel efficient engines canincrease particulate emissions. Thus, by simultaneously using port anddirect injection fuel systems during engine start, catalyst warming, andengine warm-up can be achieved while enabling low PM emissions fromengines and power trains, including turbocharged engine configurations.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described steps maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be further appreciated that the configurations and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. For example, the above technology canbe applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types.The subject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method of operating an engine,comprising, responsive to an engine cold-start and during a firstcombustion event since the engine cold-start: port injecting a firstportion of fuel during a closed intake valve event; and direct injectinga remaining portion of the fuel over multiple injections of the firstcombustion event at a first ratio of the first port injection portionrelative to a total first direct injection amount; and responsive to anengine hot-start and during a first combustion event since the enginehot-start: port injecting a second portion of fuel; direct injecting aremaining portion of the fuel over multiple injections of the firstcombustion event at a second ratio, higher than the first ratio, of thesecond port injection portion relative to a total second directinjection amount; and wherein a first direct injection ratio of intaketo compression injection during the cold-start is higher than a seconddirect injection ratio of intake to compression injection during thehot-start.
 2. The method of claim 1, wherein injecting the remainingportion of fuel over multiple injections includes injecting theremaining portion as at least a first intake stroke injection and asecond compression stroke injection.
 3. The method of claim 1, whereindirect injecting the remaining portion of fuel over multiple injectionsincludes injecting the remaining portion as multiple intake strokeinjections, multiple compression stroke injections, or at least oneintake stroke injection and at least one compression stroke injection.4. The method of claim 1, wherein the first ratio of the first portinjection portion relative to the total first direct injection amount isadjusted based on an exhaust catalyst temperature.
 5. The method ofclaim 1, wherein the first and second ratios are adjusted based on asoot load of the engine.
 6. The method of claim 5, wherein each of thefirst and second ratios are further adjusted based on a combustion eventnumber subsequent to the first combustion event.
 7. The method of claim6, further comprising retarding spark timing based on an exhaustcatalyst temperature and an engine temperature at the engine start. 8.The method of claim 7, wherein an amount of spark retard is furtherbased on each of the first and second ratios.
 9. The method of claim 1,further comprising continuing the port injecting and direct injectingover multiple fuel injections during cranking subsequent to the firstcombustion event.
 10. The method of claim 9, wherein the continuing isperformed for a number of combustion events since the first combustionevent, the number based on a cylinder event number.
 11. The method ofclaim 9, further comprising, after cranking, transitioning fuelinjection to a third ratio of port injection to direct injection, and afourth ratio of intake stroke injection to compression stoke injection,the third ratio different from the first ratio, and the fourth ratiodifferent from the second ratio.
 12. The method of claim 9, furthercomprising, after cranking, transitioning fuel injection to portinjecting a portion of fuel during a closed intake valve event anddirect injecting a remaining portion of the fuel during an intake strokeor compression stroke.
 13. A method for an engine, comprising:determining whether a start is a cold-start based on engine temperaturebelow a threshold; during the engine cold-start and while cranking,based on a cylinder event number, injecting fuel as a first portinjection during a closed intake valve event, at least one directinjection during an intake stroke, and at least one direct injectionduring a compression stroke at a first ratio of the first port injectionportion relative to a total first direct injection amount; determiningwhether a start is a hot-start based on engine temperature above thethreshold; during the engine hot-start and while cranking, injectingfuel as a second port injection during a closed intake valve event, atleast one direct injection during an intake stroke, and at least onedirect injection during a compression stroke at another ratio of thesecond port injection portion relative to the total first directinjection amount, the another ratio higher than the first ratio; andwherein a first direct injection ratio of intake to compressioninjection during the cold-start is higher than a second direct injectionratio of intake to compression injection during the hot-start.
 14. Themethod of claim 13, wherein injecting based on a cylinder event numberincludes continuing the injecting during the cold-engine start andcranking until a threshold cylinder event number is reached, and thentransitioning fuel injection to another closed intake valve portinjection and at least one intake and compression stroke injection, aratio of port injection to direct injection after the threshold cylinderevent number is reached is different than from before the thresholdcylinder event number is reached, and a second ratio of intake strokedirect injection to compression stroke direct injection after thethreshold cylinder event number is reached is different than from beforethe threshold cylinder event number is reached.
 15. The method of claim14, wherein after the threshold cylinder event number is reached, thefirst ratio of the port injection during the closed intake valve eventto the total first direct injection amount is based on an exhaustcatalyst temperature and engine temperature, the first ratio of portinjection to direct injection increased as the exhaust catalysttemperature increases.
 16. The method of claim 14, wherein before thethreshold cylinder event number is reached, the first ratio is based onan estimated engine soot load.
 17. An engine system, comprising: anengine; a first port injector coupled to an engine cylinder; a seconddirect injector coupled to the engine cylinder; and a control systemwith computer readable instructions for, during a first cylindercombustion event, injecting both port and direct injected fuel at aratio, the ratio lower at cold engine starts and higher at hot enginestarts, wherein the direct injected fuel during the first cylindercombustion event is injected over multiple injections at a ratio ofintake to compression direct injection, the ratio of intake tocompression direct injection higher during the first combustion event ofthe cold engine starts than the first combustion event of the hot enginestarts; and based on a cylinder combustion event number since the firstevent, transitioning cylinder fuel injection from a first injectionprofile including a first port injection during a closed intake valveand a second direct injection including at least one intake strokeinjection to a second injection profile including at least onecompression stroke direct injection.
 18. The system of claim 17, whereinthe first injection profile and the second injection profile are basedon catalyst temperature, engine temperature and soot load, and wherein aproportion of fuel direct injected in the compression stroke relative tothe intake stroke is higher in the first injection profile as comparedto the second injection profile.